1. Field of the Invention
The present invention relates to a device for detecting whether a liquid surface of a liquid stored in a reservoir tank is a predetermined height or more.
2. Description of the Related Art
An automatic processor for photographic light-sensitive materials comprises a plurality of processing tanks such as a developing tank, a fixing tank, a rinsing tank, a replenisher tank and the like and each of the processing tanks contains a processing solution. If the amount of the processing solution stored in the processing tank is less than a reference point, the quality of images may deteriorate. Therefore, in such a case, a replenisher should be supplied to the processing tank. However, if the processing tank comprises no auxiliary tank for collecting an overflow and the replenisher is supplied by mistake to the tank in which stores the sufficient amount of the processing solution, the processing solution may overflow the processing tank.
In order to devoid such a situation, the processing tank is equipped with a detecting device which detects the accurate position of the liquid surface of the processing solution stored in the processing tank, and various types of detecting devices have been proposed.
One of typical detecting devices is that comprising a pair of electrodes. The pair of electrodes is disposed in the processing tank and is connected electrically to an ammeter for measuring a current value passing between the electrodes which varies depending on the position of the liquid surface.
In a method using the above detecting device, although respective polarities of the electrodes are changed at a predetermined interval so as to prevent components of the processing solution from depositing on the electrodes, calcium carbonate may adhere to the electrodes depending on water quality. This results in decrease of the conductivity of the electrodes and thereby the current value cannot be measured accurately. In order to devoid such a malfunction, it is necessary to conduct maintenance such as washing of the electrodes at a relatively short time interval.
Another of typical detecting devices is that comprising a float which floats in the processing solution. In this detecting device, an angle between the float and an arm connected to the float, or a rotation number of a sprocket which winds a tape connected to the float is measured so as to calculate the position of the liquid surface.
However, in the detecting device, when components of the processing solution deposits on the float, the float may not shift smoothly or may not shift completely. Moreover, the float may blow out. In order to solve these problems, maintenance for the float should be conducted frequently.
The other of typical detecting devices is that using ultrasonic wave. In this detecting device, time between output of the ultrasonic waves to the liquid surface and receiving the ultrasonic waves reflected by the surface is measured so as to calculate the position of the liquid surface.
However, if the liquid surface almost equals to the reference point and waves, the ultrasonic wave may be reflected by a peak of waves and the replenisher may not be supplied to the processing tank. In order to solve this problem, a mechanism for preventing surface wave is needed.
The present inventors found that a measurement of the accurate position of the liquid surface is unnecessarily so as to prevent deterioration of image quality and to prevent overflow.
It is an object of the present invention to provide a detecting device which use no movable member such as a float and can detect accurately whether the liquid surface equals to or is higher than the reference point for a long period of time without maintenance even if the detecting device is disposed in the processing solution containing chemicals such as a developer.
The present invention is a device for detecting whether a liquid surface of a liquid stored in a reservoir tank equals to or is higher than a predetermined height, comprising: a transmitter for outputting sound waves; a receiver which is spaced apart from the transmitter and which converts received sound waves to electric signals having a parameter corresponding to a sound volume of the sound waves; and a comparator for outputting detection signals which show that the liquid surface coincides with or is higher than the heights of the transmitter and the receiver when parameters of the electric signals from the receiver equal to or are more than a threshold.
According to the present invention, the transmitter outputs sound waves and the receiver receives the sound waves and converts them to electric signals having a parameter, such as a voltage and a current corresponding to sound volume of the received sound waves. The liquid can transmit sound waves more easily than the air. Therefore, the parameter of the electric signals which is obtained when the liquid surface coincide with or is higher than the height of the transmitter and the height of the receiver is larger than that when the liquid surface is lower than at least one of the height of the transmitter and the height of the receiver. When the parameters of the electric signals from the receiver equal to or are more than the threshold, the comparator outputs the detection signals which show that the liquid surface coincides with or is higher than the heights of the transmitter and the receiver. Accordingly, if the device of the present invention is fixed at a reference point in the reservoir tank, an operator or a host computer can judge whether the liquid surface equals to or is higher than the reference point by checking whether the comparator outputs the detection signals.
As described above, the detecting device of the present invention has no movable member which may break down and detects not the accurate position of the liquid surface but whether the liquid surface equals to or is more than the reference point for a long period of time. Moreover, the detecting device can accurately detect even if it is disposed in the processing solution containing chemicals such as a developer and components of the processing solution deposit on the detecting device, so long as both of a difference between the threshold and the parameters of the electric signals obtained when the sound waves outputted from and received by the device pass through only the air or through the liquid and the air and a difference between the threshold and the parameter of electric signals obtained when the sound waves outputted from and received by the device pass through only the liquid are sufficiently large. Accordingly, maintenance can be omitted. Further, the detection is not affected by waves of the liquid surface.